Porphyromonas gingivalis is an important gram-negative periopathogen strongly associated with adult type periodontitis. In addition it is also found to persist in clinically healthy tissue demonstrating an ability to occupy different niches within the host environment. Lipopolysaccharide (LPS), a key component on the cell surface of gram-negative bacteria, is a potent immunomodulator that alerts the host of bacterial infection through a TLR 4 activation pathway. In our previous application we examined some of the unusual innate host defense immunomodulating characteristics of P. gingivalis LPS that suggested this LPS did not always act as a sentry for host recognition. In this first renewal application we propose to continue our studies "to more fully understand the role of P. gingivalis LPS in the innate host immune response." In the present application we will extend our observations and those of others that P. gingivalis LPS displays lipid A structural heterogeneity. Our hypothesis is that: P. gingivalis modifies the number and types of lipid A species present in response to environmental conditions. We suspect that the ability of P. gingivalis to synthesize and express multiple structurally different forms of lipid A represents a form of bacterially induced immunomodulation. This allows the bacterium to selectively evade and stimulate host cell responses in response to local environmental conditions contributing to its ability to occupy different niches in the host. To examine the hypothesis we have constructed three Specific Aims. The first Aim will develop techniques for the further characterization of multiple lipid A species in P. gingivalis and examine environmental factors in their regulation. The second Aim will examine the genetic mechanisms of how P. gingivalis lipid A diversity is generated. The third Aim will examine potential TLR mediated innate host interactions of the different lipid A species generated in Aims 1 and 2.